The present invention relates to a solar energy module and, more particularly, to a solar energy conversion module that converts solar energy into electrical energy, and to a Fresnel lens for use in such a conversion module.
Solar energy is frequently considered as a renewable alternative to the energy generated by fossil fuel that is predominantly used today. Of course, cost is a major factor in determining what source of energy to use, and one can reasonably expect that when the energy created through solar power conversion becomes cost competitive with that generated by fossil fuels, solar energy will come into wider use.
Solar energy conversion modules that convert sunlight into electrical energy typically employ photovoltaic or photoelectric cells that directly convert the solar energy into electrical energy. The amount of energy created by the cell is directly related to the amount of solar energy the cell absorbs; the amount of energy the cell absorbs is a function of both the size or surface area of the cell and the intensity or brightness of the sunlight that strikes the cell.
Relatively speaking, the photovoltaic cell is the most expensive component of a solar energy converter. Thus, increasing the electrical output of the converter by increasing the surface area of the photocells can quickly become very expensive, and other methods for increasing the intensity of the sunlight striking the photocell are usually employed. Such methods include using concentrator lenses and/or reflectors to focus the sunlight onto the photocell. See, e.g., U.S. Pat. No. 6,020,554, which utilizes a Fresnel lens (a lens having a stepped or grooved surface), in combination with reflectors adjacent the photovoltaic cell. Tracking mechanisms have also been developed that adjust the position of the solar energy converter as the sun travels across the sky so that the sun""s rays more directly impinge upon the photocell. See, e.g., U.S. Pat. Nos. 4,628,142 and 4,498,456, both of which are incorporated by reference herein.
The size of the module also affects the cost in other, less direct ways. As most solar energy converters are manufactured remote from their installation site, shipping and final assembly costs can become significant. Clearly, shipping costs can be minimized by reducing the size of the converter module, and simplification of the overall structure can be reasonably expected to reduce assembly costs, as well as the cost of the solar collector itself.
Thus, the primary object of the present invention is to provide a solar energy converter of simplified construction that more accurately focuses the sun""s rays onto the photocell.
It is a related object to provide such a solar energy converter that utilizes a single lens or primary optical concentrator for each photocell, and has no secondary optical concentrator, such as a further lens or reflector.
It is a further object to provide a unique lens configuration to be used as the primary optical concentrator for a solar energy converter that focuses solar energy with sufficient accuracy that no secondary optical concentrator is required.
These objects, as well as others which will become apparent upon reference to the following detailed description and accompanying drawings, are accomplished by a solar concentrator having a housing that supports at least one photovoltaic cell therein. A heat sink underlies the photovoltaic cell and a transparent cover, preferably glass, protects the surface of the cell. Positive and negative contacts are operatively connected to the cell to transmit the electrical energy generated thereby. A primary optical concentrator is provided in the form of a Fresnel lens. The Fresnel lens has a central facet and a plurality of adjacent facets of varying widths, the width of each successive adjacent facet decreasing in the direction away from the central facet. The radius of curvature of each successive adjacent facet increases in the direction away from the central facet. All of the facets have a peak of the same height and a valley of the same height. The Fresnel lens has a predetermined focal distance and the photovoltaic cell is supported within the housing within the focal range of the lens and at a distance from the lens that is less than the focal distance.
In a preferred embodiment, the solar energy converter comprises a plurality of Fresnel lens and photovoltaic cell combinations, each Fresnel lens having a central round facet surrounded by a plurality of concentric circular facets. The invention is also considered to comprise the unique Fresnel lens configuration by itself.